The metal present in blood is iron, which is the correct answer (option 4). Iron is an essential mineral that plays a crucial role in transporting oxygen throughout the body. It is a component of hemoglobin, a protein found in red blood cells responsible for carrying oxygen from the lungs to other tissues. Iron is also involved in various enzymatic reactions and is necessary for energy production and metabolism. Calcium (option 1) is not a metal present in blood, although it is an essential mineral for bone health. Zinc (option 2) and sodium (option 3) are also not metals present in blood. Zinc is involved in various enzymatic and immune functions, while sodium is an electrolyte important for maintaining fluid balance and nerve function.